#include <bits/stdc++.h>
using namespace std;
int a[10000001];

int main() {
	int n, b;
	cin >> n >> b;
	int sum = 0;
	for (int i = 1; i <= n; i++) {
		int m;
		cin >> m;
		a[i] = m;
		if (i == b) {
			a[i] = a[i] * -1;
		}
		sum += a[i];
	}
	cout << sum;
	return 0;
}